The present invention relates to a magnetic matrix display device and more particularly to grid electrodes for use in such a display. Yet more particularly, the present invention relates to the use of differing first grid (G1) and second grid (G2) apertures in such a display and to a combined sensor element and second grid electrode. Other aspects of the invention relate to a deflection anode having reduced capacitance, the use of a polyimide coating for the grid electrodes, the use of a compliant mounting and adjustment for a grid electrode assembly and the provision of an illuminated border on a magnetic matrix display.
A magnetic matrix display of the present invention is particularly although not exclusively useful in flat panel display applications such as television receivers and visual display units for computers, especially although not exclusively portable computers, personal organisers, communications equipment, and the like.
Conventional flat panel displays, such as liquid crystal display panels and field emission displays, are complicated to manufacture because they each involve a relatively high level of semiconductor fabrication, delicate materials, and high tolerances.
GB Patent Application 2304981 discloses a magnetic matrix display having a cathode for emitting electrons, a permanent magnet with a two dimensional array of channels extending between opposite poles of the magnet, the direction of magnetisation being from the surface facing the cathode to the opposing surface. The magnet generates, in each channel, a magnetic field for forming electrons from the cathode means into an electron beam. The display also has a screen for receiving an electron beam from each channel. The screen has a phosphor coating facing the side of the magnet remote from the cathode, the phosphor coating comprising a plurality of pixels each corresponding to a different channel.
In a colour magnetic matrix display, each of the corresponding phosphor pixels may be a group of phosphor elements, each group corresponding to a different channel and each group typically comprising a Red, a Green and a Blue phosphor element. There are first and second deflection anodes for sequentially addressing electron beams emerging from the channels to different ones of the phosphor elements thereby to produce a colour image on the screen. The first and second deflection anodes are arranged as a pair of combs. There is a significant capacitance between these combs, which means that for high speed applications such as high refresh rates or autostereoscopic displays, high current driver amplifiers must be used in place of low cost standard integrated circuit amplifiers.
There are grid electrodes disposed between the cathode and the magnet for controlling the flow of electrons from the cathode into each channel. These control grids comprise a first group of parallel control grid conductors (first grid) extending across the magnet surface in a column direction and a second group of parallel control grid conductors (second grid) extending across the magnet surface in a row direction so that each of the channels is situated at the intersection of a different combination of a row grid conductor and a column grid conductor. In operation, each of the first group of grid conductors are held at one of two fixed potentials, whilst each of the second group are driven to analog voltages that will determine the beam current which will flow.
There is a significant capacitance between the second grid conductors and the other electrodes of the display as well as to ground, which will act to slow the drive signal rise and fall time. There is also a mutual coupling capacitance between the first grid conductors and the second grid conductors, which will cause a transient on the second grid conductors when the first grid conductors is switched from one to the other of the two fixed potentials. Further there is a mutual coupling capacitance between adjacent conductors of the second grid conductors, which causes crosstalk between the channels associated with adjacent ones of the second grid conductors.
Additionally, the grid drive voltages for certain applications such as a display using a very low beam current or using a high beam current may be outside the range desirable in order to minimise the cost of the grid drivers. The second grid conductors, which are driven by digital to analog converters (DACs), should ideally be capable of being driven at CMOS compatible voltages. Too high a voltage leads to expensive drivers, such as those which are used in Plasma panels. Too low a voltage leads to excessive difficulty in controlling beam current due to sensitivity to electrical noise, DAC linearity and the like.
Co-pending GB Patent Application 961 1469.9 discloses a sensor array plate consisting of metal strips across the path of the electron beam, separate from the normal grid structure. This provides real time active beam current sensing for each channel of a magnetic matrix display. Such a structure, having an array separate from the normal grid structure is complex and has many interconnections.
Co-pending GB Patent Application 9703807.9 discloses a magnet for, a magnetic matrix display having an insulated plate located on the side facing the cathode, the surface of the flat insulated plate facing the cathode being at a predetermined distance from the control grid (first grid) and being perforated with one or more apertures for each of the one or more electron beams. Such an insulated plate and the control grids mentioned above require several processes to make and leave small gaps which are difficult to evacuate when the glass envelope is evacuated. Additionally, the grid connections must be brought out to the driver chips, located external to the glass envelope.
One of the requirements of a magnetic matrix display is to precisely align the apertures in the magnet with the phosphor stripes on the screen. If uniform column stripes are used the problem becomes one of horizontal alignment and rotational alignment. Alignment of thc structure to less than the width of one phosphor stripe is possible with the use of optical alignment aids, such as, for example, by aiming a laser through preselected apertures whilst the magnet and screen are held and adjusted in a fixture. However, some residual adjustment may be necessary after construction of the magnetic matrix display, to give optimal colour purity. Co-pending GB Patent Application 9612345.0 discloses a method by which small horizontal adjustments may be made by introducing an offset voltage onto the deflection anodes. Co-pending GB Patent Application 9625235.8 discloses a method of electronic control of rotation, but such a method requires a more complex manufacturing process for the grid assembly.
Co-pending GB Patent Application 9706992.6 discloses a magnet for a magnetic matrix display wherein the magnet extends beyond the area occupied by the array of channels such that the field strength in the channels at the periphery of the array is substantially equal to the field strength in channels at the centre of the array. This extended area is not used for the display of information due to the non-linearity of any display in this area. However, the area does produce a non-display border around the active display area, which increases the size of the display.
In accordance with the present invention, there is now provided a display device comprising: cathode means for emitting electrons; a permanent magnet; a two dimensional array of channels extending between opposite poles of the magnet; the magnet generating, in each channel, a magnetic field for forming electrons from the cathode means into an electron beam; a screen for receiving an electron beam from each channel, the screen having a phosphor coating comprising a plurality of groups of adjacent pixels facing the side of the magnet remote from the cathode, each corresponding to a different channel; grid electrode means disposed between the cathode means and the magnet for controlling flow of electrons from the cathode means into each channel; and deflection means for sequentially addressing the electron beam from each channel to each pixel of the corresponding group, the deflection means comprising a plurality of anode means each disposed on the surface of the magnet remote from the cathode, each corresponding to a different channel, and each comprising first and second anodes respectively extending along opposite sides of the corresponding channel for accelerating electrons through the corresponding channel and for sequentially addressing electrons emerging from the corresponding channel to different pixels of the corresponding group, a plurality of each of the first and the second anodes being arranged in respective groups, each of the respective groups being driven by respective drivers. The separation of the plurality of anode means into groups reduces the drive requirements of each driver, since the capacitance driven by each of the drivers is reduced.
In a preferred embodiment, the first and the second portions are arranged as four groups. This allows the use of eight drivers, a number which may be obtained from a single integrated circuit.
Viewed from another aspect, the invention provides a display device comprising: cathode means for emitting electrons; a permanent magnet; a two dimensional array of channels extending between opposite poles of the magnet; the magnet generating, in each channel, a magnetic field for forming electrons from the cathode means into an electron beam; a screen for receiving an electron beam from each channel, the screen having a phosphor coating comprising a plurality of groups of adjacent pixels facing the side of the magnet remote from the cathode, each corresponding to a different channel; grid electrode means disposed between the cathode means and the magnet for controlling flow of electrons from the cathode means into each channel, the grid electrode means comprising a plurality of parallel row conductors and a plurality of parallel column conductors arranged orthogonally to the row conductors, each channel being located at a different intersection of a row conductor and a column conductor, the parallel conductors narrowing in width between the different intersections between each of the row conductors and each of the column conductors. The narrowing in width of the conductors between intersections reduces the capacitance of the grid electrode means to other electrodes of the display and to ground.
In a preferred embodiment, at each of the intersections between each of the row conductors and each of the column conductors, the parallel conductors are substantially similarly shaped to the shape of the aperture. This shaping allows the grid electrode to perform its function, but with a minimum of overlapping area between the row conductors and the column conductors, reducing the capacitance therebetween.
Viewed from yet another aspect, the invention provides a display device comprising: cathode means for emitting electrons; a permanent magnet; a two dimensional array of channels extending between opposite poles of the magnet; the magnet generating, in each channel, a magnetic field for forming electrons from the cathode means into an electron beam; a screen for receiving an electron beam from each channel, the screen having a phosphor coating comprising a plurality of groups of adjacent pixels facing the side of the magnet remote from the cathode, each corresponding to a different channel; grid electrode means disposed between the cathode means and the magnet for controlling flow of electrons from the cathode means into each channel, the grid electrode means comprising a plurality of parallel row conductors and a plurality of parallel column conductors arranged orthogonally to the row conductors, each channel being located at a different intersection of a row conductor and a column conductor, each intersection having a corresponding aperture in each of the row conductor and the column conductor, the apertures in the row conductors and the column conductors being different in size. The differing sizes of apertures allows the DACs driving the second grid or row conductors to be within a range of voltages which is compatible with the use of CMOS technology for the drivers and also to improve the control of the beam current and reduce sensitivity to electrical noise, DAC linearity and the like.
In a preferred embodiment, the apertures in the row conductors are smaller than the corresponding apertures in the column conductors. This increases the voltage sensitivity of the second grid (the row conductors) and allows the use of lower voltage drivers for a given beam current. Additionally, the edges of the first grid and second grid do not precisely coincide meaning that an insulating layer used between the first grid and the second grid may be extended.
Preferably, the grid electrode means further comprises a first insulating layer disposed between the row conductors and the column conductors, the first insulating layer having apertures intermediate in size between those of the row conductors and those of the column conductors. The positioning of such an insulating layer can be done with a low accuracy whilst still ensuring that the first and second grid tracks do not short together.
Viewed from a further aspect, the present provides a display device comprising: cathode means for emitting electrons; a permanent magnet; a two dimensional array of channels extending between opposite poles of the magnet; the magnet generating, in each channel, a magnetic field for forming electrons from the cathode means into an electron beam; a screen for receiving an electron beam from each channel, the screen having a phosphor coating comprising a plurality of groups of adjacent pixels facing the side of the magnet remote from the cathode, each corresponding to a different channel; grid electrode means disposed between the cathode means and the magnet for controlling flow of electrons from the cathode means into each channel and having a sensor electrode located thereon. The use of a combined sensor electrode and second grid structure reduces the complexity and the number of process steps as well as the number of interconnections from the sensor electrode to the second grid.
Viewed from yet another aspect, the present invention provides a display device comprising: cathode means for emitting electrons; a permanent magnet; a two dimensional array of channels extending between opposite poles of the magnet; the magnet generating, in each channel, a magnetic field for forming electrons from the cathode means into an electron beam; a screen for receiving an electron beam from each channel, the screen having a phosphor coating comprising a plurality of groups of adjacent pixels facing the side of the magnet remote from the cathode, each corresponding to a different channel; grid electrode means disposed between the cathode means and the magnet for controlling flow of electrons from the cathode means into each channel, the grid electrode means being formed on a polyimide substrate. The use of a polyimide substrate and double sided circuit construction techniques simplifies the construction of, and reduces the fragility of the grid assembly. Additionally, grid aperture dimensions of differing sizes may easily be used. Polyimide may be applied as a conformal polyimide coating thus removing any small gaps which would otherwise be difficult to evacuate.
In a preferred embodiment, the grid electrode means and the substrate extend beyond the two dimensional array of channels. Preferably, the display device further comprises an enclosing glass envelope and the grid electrode means and the substrate extend through the glass envelope. Further preferably, grid electrode driver chips are attached to the substrate.
More preferably, the display device further comprises a polyimide second insulating layer between the grid electrode means and the magnet. Yet more preferably, the display device further comprises a third polyimide insulating layer between the grid electrode means and the cathode. Preferably, a conducting film is present on the side of the third insulating layer facing the cathode. Further preferably, the conducting film is gold. The conducting film is a good reflector of infrared radiation from the cathode filaments and can reflect most of the heat away from the polyimide and the magnet.
In a preferred embodiment, the magnet is a photomachineable magnet and the substrate forms an exposure mask for the photomachinable magnet. This simplifies the photomachining process for producing the apertures in the magnet.
Also, in a preferred embodiment, the display device further comprises a through-glass magnet position adjustment. This allows the precise alignment of the apertures in the magnet with the phosphor stripes on the screen. Preferably, the position adjustment causes rotation of the magnet with respect to the screen. If uniform column stripes of phosphor are used, then only horizontal and rotational alignment are needed. Horizontal alignment may be made simply by introducing an offset voltage onto the deflection anodes. Rotational alignment can be by means of the through-glass magnet position adjustment. More preferably, the adjustment is a screw and the screw is located within a crushable metal housing. A crushable metal housing is suitable since the adjustment is a once only manufacturing setting.
Viewed from a further aspect, the present invention provides a display device comprising: cathode means for emitting electrons; a permanent magnet; a two dimensional array of addressable channels extending between opposite poles of the magnet and a plurality of border channels extending in at least a first dimension beyond the area occupied by said two dimensional array of addressable channels; the magnet generating, in each channel, a magnetic field for forming electrons from the cathode means into an electron beam; a screen for receiving an electron beam from each addressable channel, the screen having a phosphor coating facing the side of the magnet remote from the cathode, the phosphor coating comprising a plurality of pixels each corresponding to a different addressable channel; grid electrode means disposed between the cathode means and the magnet for controlling flow of electrons from the cathode means into each addressable channel; wherein said screen has a phosphor coating corresponding to said border area channels. The magnet in the display is larger than the array of addressable channels used for the active display because of the need to improve the linearity of addressable channels near to the periphery of the magnet. The provision of an illuminated border reduces the apparent effect of the larger magnet on display size.
In a preferred embodiment, the phosphor coating forming the illuminated border is a single colour. This avoids the problems of adjusting the colour point of multiple phosphor colours and of purity errors due to the magnetic field non-linearity in this area.
In an alternative embodiment, the phosphor coating comprises a plurality of pixels having adjacent elements of differing colours; and the display device further comprises deflection means for sequentially addressing the electron beam from each channel to each element of the corresponding pixel. Preferably, the first grid for the border area is modulated. This allows precise adjustment of the colour point displayed to any colour within the region bounded by the phosphor colours. Alternatively, the adjacent elements in a pixel each receive the same beam current and the dimensions of each of the adjacent elements in a pixel are chosen so as to produce light of a pre-defined colour.
The present invention extends to a computer system comprising: memory means; data transfer means for transferring data to and from the memory means; processor means for processing data stored in the memory means; and a display device as claimed in any preceding claim for displaying data processed by the processor means.